In drilling directional bores in the earth, as for gas or oil wells, it is necessary to establish as accurately as possible the deviated course to be followed and to orient the down-hole tools to maintain this course. Further, the ultimate horizontal displacement of the borehole must be accomplished by smooth, gradual course changes in order to facilitate the smooth casing of the borehole to complete the well.
The rig system conventionally employed comprises a surface drilling assembly and a down-hole assembly including a pipe string of drill pipe sections supporting a distal drilling assembly comprising a drill collar weighting a rotational drill bit, and an orienting sub and bent sub which establish the angle of deflection of the drill bit. The down-hole assembly for directional bores further typically includes a down-hole motor such as a mud motor which drives the drill bit and which is operated by drilling fluid circulating within the pipe string; the use of the mud motor thereby obviates rotatonal motion of the entire down-hole assembly which would further complicate the engineering of the directional bore.
Originally, the desired course of the directional bore was established by the "single-shot" survey method wherein a survey is made on each section (usually 30 ft.) of drill pipe as it is drilled down into the borehole, and the drilling assembly reoriented as required. Dissatisfaction with the time-consuming nature of this method and its inaccuracy in deeper boreholes led to the development of an electronic steering system for surveying and orienting the drilling assembly under dynamic (drilling) conditions. The steering system typically includes a down-hole tool or probe which engages within the orienting sub and transmits bottom-hole survey and orientation information such as tool setting ("tool-face"), hole angle, and hole direction to surface readout equipment via electronic impulses along a wire line or "logging line" contained within the pipe string. By correcting aberrant deflections of the drill bit reflected in the surface readout equipment, proper torque balance of the down-hole assembly may thus be obtained, and the directional borehole drilled more smoothly and accurately than previously possible.
With the advent of the electronic steering system, revision of the conventional surface drilling assembly was necessary to accommodate the wire extending through the pipe string to the surface readout equipment. Previously, the surface drilling assembly included a kelly or hollow drive shaft, of the type described in U.S. Pat. No. 3,848,684 to West, selectively engaged with a rotary table by a kelly drive bushing disposed on the table so that rotary motion of the table is imparted to the kelly. In this assembly, the kelly is releasably engaged with the upper end of the drill pipe string so that the bore of the kelly communicates at one end thereof with the drill pipe string, and at the other end thereof with a kelly hose which is a conduit for drilling fluid contained in storage devices such as tanks. In operation, the drilling fluid is pumped from storage through the kelly hose, the kelly, and through the drill pipe string to operate the down-hole motor. After exiting through the drill bit, the fluid then rises through the annular space between the pipe string and the bore hole to the surface where it is collected and directed to the storage tank, via a flowline, for recirculation.
With the electronic steering system, it is necessary to "pack off" or seal the wireline, to prevent the escape of drilling fluid at the point where the wireline diverges from the drill pipe string to the surface readout equipment. Since the wireline cannot be run through the kelly and then packed off, in order to use the electronic steering system with circulating drilling fluid, it has heretofore been necessary to remove the kelly from the surface drilling assembly and replace it with a pack-off unit at the top of the drill pipe string. This is done by removing the kelly hose after circulation of the drilling fluid has been halted, replacing the kelly with a pack-off unit, running the wireline through the pack-off unit, and attaching the kelly hose to the unit. Drilling fluid can then be circulated after the pack-off is tightened about the wireline.
Removing the kelly from the line in this manner has several disadvantages. For one, it is time-consuming, and for another, it is hazardous to the drilling operation, as with the cessation of circulation of the drilling fluid and the necessary location of the drilling assembly within about ten feet of the bottom of the hole during the operation, the potential for the drilling assembly to become firmly lodged in the hole greatly increases. Further, in typical drilling rigs, only ninety feet of hole can be drilled after the kelly is replaced, since the derricks employed can only hoist ninety feet of drill pipe above the surface because of limitations imposed by the length of the kelly hose and associated conduit for the drilling fluid. Thus, when the packed-off drill pipe has been drilled down, the entire operation must again be halted while the fluid circulation is stopped, the pack-off unit removed, the wireline pulled, and more pipe added on the string.
While the system has been improved by the development of the side-entry sub of the type described in U.S. Pat. No. 4,062,551, this innovation has still not permitted retention of the kelly in place in the surface drilling assembly simultaneously with the employment of the electronic steering system. A hollow cylindrical component of the drill pipe string, the side-entry sub is customarily engaged with the uppermost section of the drill pipe at the rotary table and is adapted to receive the wireline through a radially extending bore or channel in the side-entry sub. The wireline can then be packed-off where it enters the side-entry sub and the drilling can proceed uninterrupted as the wireline is extended within the borehole annulus adjacent the pipe string to the desired length, without the necessity of periodically pulling the wireline to add further sections of drillpipe.
Notwithstanding this advantage, it has not been possible to employ the kelly in conjunction with the side-entry sub owing to the path the wireline follows after exiting the side-entry sub. Typically, at present, the wireline passes to the surface of the borehole from the side entry sub alongside the pipe string, to which it is secured at intervals, through an aperture in the center of the rotary table to a sheave or pulley associated with the derrick, and from there to the wireline unit and then to the surface readout equipment. With the kelly drive bushing disposed in its usual position on the rotary table, the wireline would be cut or damaged by the bushing, with resultant steering system failure. Accordingly, the kelly is not presently used with the side-entry sub, and as a result, the use of the electronic steering system even with the side-entry sub necessitates the removal of the kelly with the accompanying removal and reconnection of the kelly hose while the drill assembly is on bottom, with the attendant risks and delays described supra. Further, the absence of the kelly makes it more difficult to apply torque to the drill pipe string as necessary, for example, to correct the orientation of the drilling assembly when the mud motor is being employed.
Accordingly, it is an object of the invention to provide means for adapting a kelly drive bushing to accommodate a steering system wireline without appreciably endangering the integrity of the wireline.
It is a further object of this invention to provide means for adapting a kelly drive bushing to accommodate a steering system wireline to permit the concurrent use of an electronic steering system and a kelly and kelly drive bushing in the directional drilling of a borehole.
It is another object of this invention to provide means for adapting a kelly drive bushing to safely accommodate a steering system wireline, which means are removably engageable with the kelly drive bushing whether or not the kelly is engaged with the drill pipe string.
It is a further object of this invention to provide means for adapting a kelly drive bushing to accommodate a steering system wireline which will permit the kelly and kelly drive bushing to freely rotate as necessary to engage added sections of drill pipe without entangling of the steering system wireline.
It is also an important object of this invention to provide means for adapting a kelly drive bushing to safely accommodate a steering system wireline to obviate the necessity for periodic removal of the kelly during the drilling of directional bores with the aid of an electronic steering system and the associated necessity of removal and reconnection of the kelly hose to the pack-off unit which customarily replaces the kelly in the surface drilling assembly.
It is yet another object of this invention to provide means for adapting a kelly drive bushing to accommodate a steering system wireline without interruption of drilling fluid circulation during installation thereof.
Further objects and advantages of the invention will be apparent from the following description and drawings.